Composite antenna structure



Oct. 30, 1956 A. M. CLOGSTON 2,769,170

COMPOSITE ANTENNA STRUCTURE Filed May 29, 1952 5 Sheets-Sheet 1 F/G. b4F/G. /B

EL scmoma/vsr/c cu/mwr E 0 oa/vs/ry l I g [471/ 0mcnoor J PROPAGATION OFFIG. 2A fgygGA/U/c ELECTRIC VECTOR CURRENT DENS/TY CURRENT DENS/TY METALOR D/ELECT/P/C lNl EN r09 4. M CLOGSTON ATTORNEY Oct. 30, 1956 A. M.CLOGSTON 2,769,170

COMPOSITE ANTENNA STRUCTURE Filed May 29, 1952 5 Sheets-Sheet 2 a gtA200 0 4 5 /.O $3 .8 L] 9Q .6 Q E 1 Q 2 3 4 5 E D/ELECTR/CCON$7;4NT(6)OF INSULAT/NG MED/UM- BETWEEN INNER AND 0U T ER CONDUC T OPS/Nl/ENTOR A. M CLOGSTO/V ATTORNEY Oct. 30, 1956 A. M. CLOGSTON 2,759,170

COMPOSITE ANTENNA STRUCTURE Filed May 29; 1952 5 Sheets-Sheet a FIG. 6FIG. 7A

METAL R DIELECTRIC :30- 3 FIG. 8

l\ g 5 E 0 x I l 44 t 0 /0 t FREQUENCY f-IN MEGACYCLES PER SECOND //vVENTOR ,4. M. CLOGSTON ATTORNEY Oct. 30, 1956 A. M. CLOGSTON 2,769,170

COMPOSITE ANTENNA STRUCTURE Filed May 29,- 1952 5 Sheets-Sheet 5 CURRENTDENS/TY RAD/AL DISTANCE MEML 0R DIELECTRIC FIG. /6

mac I508 MA TCH/NG /50C DIELECTRIC INVENTOR A. M CLOGS TON ATTORNEYUnited Stat PatentC) COMPOSITE ANTENNA STRUCTURE Albert M. Clogston,Morris Plains, N, J., assignor to Bell Telephone Laboratories,Incorporated, New York,

N. Y.,'a corporation of New York I Application May 29, 1952, Serial No.290,805 13 Claims. Cl. 343-907 This invention relates to antennas andhas as'one of its principal objectives the improvement of antennas withrespect to skin effect. This application is a continuation-' in-partofapplication Serial No. 214,393, filed March 7, 1951.

Due to the phenomenon known as skin effect, at high frequencies thecurrent distribution through a conductor is not uniform. Consider, forexample, the case ofa two-conductor coaxial line to which are appliedwaves of increasing frequency. At zero and sufiiciently low frequenciesthe currents in the conductors are substantially uniformly distributedthroughout and the resistance of the conductors and hence the conductorloss in the line is'at a minimum. With increasing frequency the currentdistribution changes so that the current density is a maximum at theinner surface of the outer conductor and at the outer surface oftheinner conductor and decreases into the material at a rate'dependingon the frequency and the material. In the examplegiven the currentdensity may be negligible at the other surface of each conductor. Fromanother point of view, the electromagnetic field between the twoconductors (Where the useful power is transmitted) penetrates into theconductors'with a field intensity decreasing with distance. Thus thecurrent density (or field) in each conductor isassociated with ;a powerloss that is a function of the distribution of current density (orfield) across the-thickness of the;

conductor.

It is thus a more particular object of this invention to reduce thepower loss associated with skin effect in electricalconductors andparticularly, to conductors utilized in antenna systems.

Further objects of the invention are to reduce the extent to which thepower loss in such a conductor varies' with frequency, and to make suchpower loss and conse-. quently its contribution tothe attenuation-.of-an antenna made up of such conductors substantially independentoffrequency over a broad. band of frequencies from the,

lowest frequency of interest to the highest. For example, in practice,"such a band might becomparatively narrow or alternatively might besufficiently wide as to accommodate nels. I I I This invention, in oneof its more important aspects", resides in a'composite electricalconductor 'for antenn as that is separated transverse to thejdirectionof desired Wave energy propagation, into a multiplicity of insulatedconducting elements of suchnumber, dimensions and disposition relativeto each other and the orientation of the,- electromagnetic waveastoachievea more favorable'dis-w tribution of, ,current -.and fieldwithin the conducting.

material. 7

In'the case of bothof the conductors isformed, in accordancewith theinvention, of. a multiplicity of thin metal lamiuations insulated fromone another by layers ofinsulating material,

the smallest dimension of the l aminations being in the directionperpendicular to both the direction of wave a plurality of wide-bandtelevision char1-' vthetwo-conductor coaxial line, one or,

"ice 1 propagation and the magnetic vector. A convenient: yardstick inreferring to thethickness of-the metal l'am'inations and of theinsulating layers is the distance 6 given 6- j'lrfud where 6 isexpressed in meters, 3 is the frequency in cycles per second, 1. is thepermeability of the metal in henries permeter, and dis the conductivityof the metal in The factor 5 measures the-distance. in which the'currentor field penetrating into a slab or the metal" per meter.

many times 6 in thickness' will decreaseby one neper; i. e., theiramplitude will become equal to 1/e=0.3679 timestheir'am Iitude at thesurface ,of the slab This factor 8 will be called one skin thicknesslorone skin depth. In the case being considered, it is contemplated'thatthe thickness of each lamination is many times (for example, 10,100 oreven'1000 times) smaller than 6 (in general, the thinner the better) andthatjthere will be many laminations (for example, 10, 50, or more). Ithas been found that when the conductor has such a laminated structure, awave'propagating along the conductor at a velocity in the neighborhoodof a certain critical value will penetrate further into the conductor(or completely through it) than it would penetrate into a solidconductor of the same material. This results in a more uniform currentdistributionin the laminated conduc'tor and consequently lower, losses.Another way of looking at this result is'to say thatthe effective skindepth is much larger in the laminated conductor than the,

skin depth 6 for a solid conductor of'the same material as thelaminations. c l

The critical velocity mentioned above is determined by the thickness'ofthe metal and'ins'ulating laminae, and the dielectric constant of theinsulating laminae, The

electromagnetic wave can be caused to propagate in the neighborhood ofthis critical velocity by a variety of means including (for example) theproper disposition'of' dielectric material in the vicinity of theconductor. -By way of example, in one form of coaxial cable which isutilized in an antenna system constructed with the raven: tionythat is,in the case of two laminated concentric, conductors (each comprising amultiplicity of metal laminae thin compared to 6 separated by thininsulating layers) which are separated fromeach other by a maindielectric,

the wave propagates at the critical velocity if the dielectric constantof the main dielectric is given where s is the dielectric constant ofthe main dielectric element between thetwo c'onductors in farads permeter, 6, is the dielectric constant of the insulating material betweenthe laminae of the conductors in farads permeter, W is the thickness ofone of the metal laminae in meters, and t' is' the thickness of abinsulating layerin meters. The insulating layers are also made verythin, and an optimum-'thickness'for certain types of structures m re.cordance with tl 1e"inv er1tion (as will be described more with theaccompanyingdrawingsforming a part thereof,

in which? Fig. 1A is a schematic representation of an electrowas; Oct.30, 1956 magnetic wave propagating through space in the neighborhood ofan electrical conductor; i

Fig. 1B is a graph of current density vs. depth (distance away from thesurface) in the conductor of Fig. 1A;

Fig. 2A is a schematic diagram showing respectively th'e'directions ofelectric and magnetic field vectors-and thedirection of propagationofanelectromagnetic wave near the surface ofa. composite conductor inaccordance with the invention;

Fig. 2B is a graph having the same coordinates as in Fig. 1B, andshowing the increased skin depth produced by the conductor of Fig. 2 ascompared with that of Fig.1A;. a

Fig'. 3A is an end view of a coaxial transmission line which is utilizedinvarious forms of, antennas in accordance. with the invention, theinner conductor of the. line comprising a multiplicity of metallaminations insulated from one another and the inner, and outerconductors being separated'by dielectric material;

Fig; 3B'isa diagrammatic representation showing the distribution ofcurrent inthe inner and outer conductors of the embodiment shown in Fig.3A;

fFig. 3C isa longitudinal view, with portions thereof in s'ection,Yofthe'embodiment shown in Fig. 3A, a continuous dielectric being usedbetweenthe inner and outer conductors; V v

Fig/SD is a' longitudinal cross-sectional view of a section of a cableof the type shown in Fig. 3A, except that, the dielectric materialbetween the inner and outer conductors only partially fills the .spacetherebetween;

"Figj4 is a graphof attenuation vsdielectric constant of 'theinsulatingmedium between the inner and outer conductors of (A) a-coaxial cable ofthe type shown in Fi'gQZlAand (B)' a coaxial cable of aconventionaltype; F igl 5 is a longitudinal.view,.with portions in crosssection, offa modification of the embodimentshownin Fig. 3C in whichthcouter conductor is shaped to reduce the velocity of propagation;

. Fig. 6 is anend view of another form of coaxial cablewhich is utilizedin other formsof antennas in accordance with the invention, the outerconductor comprising a multiplicity of metal laminations separated byinsulat-- ing material and the inner conductor being of a conventionalform, the outer and innerconductors being separated bydielectricmaterial; I r

Fig. 7A is anend view of still another form of coaxial cable which canbe utilized in' antennas in accordance with theinventiomin material; vFig. '7B is a longitudinal view, with portions in cross section, of Fig.TA;

Fig. 8 is a graphical representation showing the at tenuation as afunctionof frequency (A) of a cable of the type shown in Fig. 7A and (B)of a standard coaxial cable of the same outer dimensions;

Fig; 9 is across-sectional. longitudinal a laminated .center conductoras shown in Figs. 3A and3C; I a H Fig; 10 is a cross-sectionallongitudinal view of a modification of the antenna of Fig. '9; i

Fig.. 11 is a perspective view of a modificatio n of the arrangement ofFig. 2A in which a multiplicityof-filamentary rods of irregular size,shape and disposition replaces the laminated structure; v Fig. 12 is anend view of a two-conductor line forming partof an antenna system inaccordance with the in-ven-- which both inner and outer conductors arelaminated and areseparated by dielectric.

a section of cable of the type-shown inv N view of an an- 7 tenna systemin accordance with the invention utilizing.

4 I i Fig. 14 is an end view of another form of coaxial cable which canbe used in antennas in accordance with the invention, ,in which allofthe space between, ansouter.

sheath and an inner core is filled with metal laminations insulated fromone another;

Fig. 15 is a graphical representation showing the approximate variationof current density with radial distance in the structure of Fig-1,4; and

Fig. 16 is a cross-sectional longitudinal view of an antenna system inaccordancewiththe inventionutilizing a laminated structure of the typeshown in Fig..,14..

Referringmore particularly to. the drawingsyconsider an electromagneticwave propagating through space" in the neighborhood of, and parallel tothe surface of an electrical conductor such as copper, silver oraluminum, for example. This situation is shown. diagrammatically inconnection with the conductor 10 in Fig. 1A which can be representativeof many phenomena. It can illustrate, for instance, the transmission ofan electromagnetic wave through a coaxial line, or along an open orshielded twowire system,-.or a wave propagating through a metal waveguide. It can alsorepresent the. situation in the vicinity of atransmitting or receiving antenna; Clearly a very broad class ofelectrical phenomena involving the transfer or periodic oscillation ofelectromagneticenergy in the vicinity of electrical conductors isrepresented in Fig.'1A.-

rent flows-ina thin layer I163! the surface.- The distance 1 from thesurface at which the current density has fallen-- to .l/e=0.3679 timesits valueuat' the surface is.

known (as mentioned above) as the skin depth and isdenoted by 6.-- Thedistance is expressed in terms of the.

frequency. (F under consideration and the permeability (a) andconductivity ((7) of the metal in Equation 1 above.-

With agiven amplitude of the electromagnetic wave, the amount of powerlost to the metal .will be proportional to-l/6a. Referring to Equation1, it can be seen that the powerless is proportional to 1/ /a s'o thatnormally the power loss is minimized by choosing a metal of high'conductivity, such as copper or silver. I

Suppose that'it were possible to arbitrarily increase without-greatlychanging 0'. It is clear that in such a-. situation the power loss fromthe electromagnetic wave' would be greatly decreased.- It has beendiscovered that. it is possible to do just thisthing,'and the presentinven-' tion is based on this discovery. ;A simple embodiment willbeconsidered first and then more general cases willbe discussed.Referring toFig. 2A, there is again shown? an electromagnetic'wavepropagating near, the surface. of an electrical conductor 20. Therelationship of'the. electric and magnetic vectors and of the directionof.

propagationof the electromagnetic wave are shown.

The conductor in Fig. 2A is no longer 'a solid piece of.

metal butiscomposed of many spaced laminae 21 of metal of thickness Warranged-parallel to. the direction:

of --,propagationfiand parallel to the magnetic vector as shown. Theselaminae .are very thin compared to 6 and are separated by empty space orany appropriate dielectric- 22 such as air, polyethylene, polystyrene,quartz, or polyfoam, for example, thethickness thereof beingrepresented' by t. Wh-ate'ver the'dielectric is, suppose that-itsdielectric constant is 6 and suppose that the conductiv ity ofthemetalis o, as before. Fig. 2A'is representative of many situations ofwhich, a few will be indicated later. The particular cases being.considered in which the magnetic vector is, parallel to the surfaceof'the com =e (1+W/t) farads per meter (3) An electromagnetic wavepropagates in a material of dielectric constant e and permeability ,uwith a velocity I/VJ T Let it now be assumed that it has been arrangedthat the electromagnetic wave in Fig. 2A is traveling with the velocityan electromagnetic wave will have in a medium of dielectric constant 2and permeability n This condition can be arranged by properly disposingsuitable dielectric material in all or part of the region traversed bythe wave outside the stack. The condition can also be fulfilled byproperly shaping adjacent electrio-a1 conductors, and a particularlyadvantageous way of bringing about this condition will be describedlater in connection with Fig. 5.

Under the conditions mentioned, if W-is small compared to 6, we candefine an efiective skin depth 6 by We can now form the term and findthat it is given by 1 i 5 zr, 0'6

It is immediately observed that the power lost frorn the electromagneticwave has been reduced by a factor For instance, if the laminae in atypical case are skin depth thick, the power taken from the wave will beonly of the power that would be lost to a solid conductor.

The increased skin depth described above not only is effective ingreatly reducing conductor losses, but has a further major concomitantadvantage. Referring to Equation 1 it can be seen that conductor lossesgenerally increase as the square root of the frequency This variationwith frequency very often is equally as troublesome as the lossesthemselves. A simple but extremely wasteful way to reduce this effect isto make the metal conductor very thin. Suppose for instance that theskin depth is B at the highest frequency under consideration. if theconductor is no thicker than 5 the losses will clearly remain uniform,but high, from very low frequencies up to this maximum. Similarly, withthe arrangement of Fig. 2A the size of the stack can be limited to thethickness 6,, determined by Equation 4 at the highest frequency, andthereby obtain uniform loss. But since 6 may be made as large asdesiredby making W small enough, this uniform loss can be achieved withoutaccepting greatly increased losses at the lower frequencies. The generalsituation'indicated'in Fig. 2A can have 6 many specific embodiments andvariations of which a few will now be described.

In Figs. 3A and 3C there is shown, in end view and longitudinal view,respectively, with portions in cross section, a coaxial transmissionline 30 constructed in a conventional way except that the innerconductor 31 is formed of many thin coaxial laminations of metal 32 andof some suitable dielectric 33. The region between the inner and outerconductors 31 and 34 is filled with insulating material 35 of dielectricconstant equal to theaverage dielectric constant of the stack asdescribed above and in Equation 3. Fig. 3B shows the approximatedistribution of current in the inner and outer conductors 31 and 34. Thecurrent is observed to decrease rapidly with distance into the solidouter conductor 34 tandmuch more slowly into the laminated innerconductor 31. Because the current falls off more slowly with distanceinto the inner conductor than it would if the inner conductor weresolid, the attenuation of the transmission line is much less than itwould be with the conventional solid inner conductor which usually has alarger resistance than the outer conductor. The line in Fig. 3A isshown'with an inner core 36. This core in specific in stances can bemetal or dielectric or even be omitted altogether. The dielectricmaterial 35 shown might equally well fill only part of the regionbetween inner and outer conductors (as shown in Fig. 3D wherein thedielectric 37 takes up only a portion of the space between the inner andouter conductors) and would have in that case a larger value than thatdescribed in Equation 3. The dielectric 37 may be held in place byspacers 38, if desired, and may be in the form of one or more dielectriccylinders surrounding theinner conductor.

' By way of example, the behavior of a specific line of the typedescribed above is shown in Fig. 4. The line has a core "of insulatingmaterial 0.146 inch in diameter. On this core are laminated 50 layers ofinsulation each 0.976 l0- inch thick and 50 layers of copper each 0.l97l0 inch thick. The overall diameter of the inner conductor is 0.264 inchand the inner and outer diameters of the outer conductor are,respectively, 4.000 and 4.166 inches. Fig. 4 compares the attenuation ofa selected length (94 /3 inches) of this line (curve A) with that of aconventional line (curve B) having a solid inner conductor of the samediameter, as the dielectric constant of the insulating material betweenthe inner and outer conductors is varied. The attenuation of the newline is seen to reach a minimum for 6:2, where E has the value given inEquation 3, and this minimum value is much less than that of theconventional line. Even for values of e appreciably diif-erent than 2(as shown in Fig. 4), the new line has advantages over the conventionalone.

Fig. 5 is a longitudinal view of a transmission line 40 somewhat similarto that shown in Fig. 3A. This example indicates how the velocity of thewave in the line can be adjusted to the proper value by appropriatelyshaping the outer conductor 41 (in a manner well known) to reduce thevelocity of propagation. This arrangement is equally as effective asthat shown in Fig. 3A in achieving reduced transmission losses. Theinner conductor 42 is similar to the inner conductor 31 of thearrangement of Fig. 3A. The core 46 is similar to the core 36.

In Fig. 6 is shown another possible embodiment 50 of the invention inwhich a stack of insulated metal laminations makes up the outerconductor 51. The inner conductor 52 can be a solid or tubular conductorand it is separated by a dielectric 53 from the laminated outer con-.ductor 51 comprising alternately disposed metal and insulating layers 55and 56, respectively. A sheath 54 of metal or other appropriate materialor combination of materials, surrounds the outer conductor 51 forshielding purposes.

J In Figs. 7A and 713 still another arrangement is illustrated,comprising a laminated inner conductor 61 of alternately disposedlaminations of metal and insulating material 66 and 67, respectively,separated by a main dielectric 63 from an outer conductor 62 which isformed of similar laminations 68 and 69, respectively. A sheath 65surrounds the outer conductor. The dielectric constant of the maindielectric 63 is made equal to e2(l+W/t) where 62 is the dielectricconstant of the laminations 67 and 69, W .is the average thickness of ametal lamination 66 or 68, and t is the thickness of an averagelamination 67 or 69 of insulation. By choosing proper values of 62, Wand t, the average dielectric con stant Eof each stack (61 and 62) canbe made equal to one another although the 52, W and t of one stack maybe different from that of the other.

Again by way of example, the behavior of a specific line of the typeshown in Fig. 7A is shown in Fig. 8. This line has a dielectric core 64of diameter .066 inch and carries a stack 61 of 50 layers of copper 66and 50 layers of insulation 67 each .0001 inch thick. The outerconductor 62 has an inner diameter of 0.330 inch and also carries astack of 50 l-aminations each of metal and insulation similar to that ofthe inner conductor. The dielectric constant of the material 63 betweeninner and outer conductors is adjusted to the optimum value given inEquation 4. Fig. 8 shows the attenuation (curve A) of this cable 60 as afunction of frequency from to 50 megacycles per second. Also shown isthe attenuation curve (curve B) for a conventional, airfilled coaxialline of nearly the same dimensions (diameter of inner conductor 0.1000inch and inside diameter of outer conductor 0.375 inch). The decreasedattenuation and less rapid variation with frequency are clearlydemonstrated.

With the cables shown in Figs. 3A, 6 and 7A there exists an optimumproportioning of the thickness of the metal and dielectric lamina. Forbest results, each dielectric lamina is made one-half the thickness of ametal lamina, or, in some specific instances, greater than half thisthickness.

Fig. 9 is a longitudinal cross-sectional view of an antenna structureembodying, or which is adapted to be connected to, a composite conductoror cable of the type shown in Fig. 3C. In the antenna of Fig. 9, theshield 34 is terminated in the form of a flat circular plate 34A havinga central aperture therein and extending but a distance approximatelycorresponding to a quarter wavelength in the dielectric of the frequencyto be radiated. The central composite conductor 36A comprising a core 36(which may be omitted) and a stack 31 of alternately disposed layers ofmetal 32 and insulation 33 is continued on past the plate 34A throughthe central opening therein for a distance approximately a quarter of awavelength in the dielectric of the frequency to be propagated from theantenna. Surrounding this central extended portion 36B of the conductor30 is a mass 35A of the same material as the main dielectric member 35of the cable 30. The mass 35A may have its end rounded off as shown inthe drawing. The radiation pattern from the antenna of Fig. 9 is similarto that of corresponding antenna systems employing solid conductors. Thestructure of Fig. 9, however, has the advantage that the power loss inthe antenna structure itself is reduced because of the reduction of skineffect losses and also has the further advantage that it can be readilycoupled to antenna lead-ins of the laminated type which also have agreatly reduced attenuation of skin effect losses.

The structure shown in Fig.10 is similar to the arrangement of Fig. 9except that instead of the sheath 34 terminating in a circular 'flatplate 34A it is instead terminated in a circular skirt 34B of a lengthapproximately onequarter wavelength in the dielectric of the frequency.to be radiated. As in Fig. 9, the central portion 36B of the compositeconductor extends past the beginning of the skirt by approximatelyone-quarter wavelength in the dielectric of this frequency. Except forthese differences the structure of Fig. is like that of Fig. 9. Theradiation. pattern from the structure 10 is different from that of Fig.9 and corresponds to the radiation pattern of a folded dipole antennaconstructed in substantially the same way except that solid elements areused. The advantages of the arrangement of Fig. 10 are similar to thoseof the antenna of Fig. 9.

In Fig. 2A there is shown drawn in perspective a laminated conductor 20made up of alternately disposed metal layers 21 and insulating layers22. It is clear that a similarly effective arrangement of conductorswould be that in which each metal lamination is divided into a series ofrectangular rods spaced by insulation. It is now also clear that therods need not be regularly arranged and indeed need not be evenrectangular in section. The conductor could in fact be composed as shownin Fig. 11 of an irregularly arranged group B of conductors of irregularcross section spaced from one another by some suitable solid dielectric96 or air or vacuum. In fact, all that is required in order that theconductor 90B in Fig. 11 be as effective as the laminations 21 in Fig.2A for reducing conductor losses is that each of the individualfilamentary 95 conductors have a maximum dimension in the direction ofthe electric vector small compared to 6. Under those circumstances abundle of filamentary conductors as Fig. 11 may replace the laminationsin the examples given in Figs. 3A, 5, 6 and 7A.

Suppose now the further step is taken of requiring the filamentaryconductors 95 to have the largest dimension in any directionperpendicular to their length small compared to 6. It is now no longerrequired that the magnetic vector be parallel to the surface of thecomposite conductor. Under these circumstances other specificembodiments of the invention can be considered.

For example, in Figure 12 there is shown a two-conductor transmissionline 100 of a type in common use with each of the conductors 101 and 102constructed as shown in Fig. 11. Substantial improvement in performanceover the conventional two-wire system can be expected. Suitabledielectric 103 is shown joining the two composite conductors 101 and 102so that the electromagnetic wave will propagate along the system with avelocity appropriate to the average transverse dielectric constant ofthe bundles.

Fig. 13 shows a simple dipole antenna which is illustrative of much morecomplicated antenna systems. The antenna is provided with compositeconductors 141 and 142 of the filamentary type shown in the last twofigures and these conductors are encased in appropriate dielectricmaterial 143 chosen to provide the proper velocity of wave propagation.The conductors 141 and 142 are fed to the antenna through a conductor ofthe type shown in Fig. 12, that is, the two composite conductors 141 and142 when outside the dielectric 143 are separated by a dielectric member144 (similar to the central dielectric member 103 in Fig. 12). The ends145 and 146 of the composite conductors 141 and 142 are then conductedto any desired transmitting apparatus. It is to be understood that thedielectric member 144 between the conductor 141 and 142 may be as longas required (the length being determined by the length of the lead-infor the antenna). The radiation pattern of the structure of Fig. 13 issimilar to that of dipoles employing solid elements but the loss is lessand ready coupling to a lead-in of the type of Fig. 12 is afforded.

In all the examples of the invention so far considered, special meanshave been provided to assure that the velocity of propagation of theelectromagnetic wave along the system is appropriate to the averagetransverse dielectric constant of the composite conductors. It has beenpointed out that under these conditions the currents penetrate deeplywithin the composite conductor. It is of course then that theelectromagnetic wave itself penetrates equally deeply into theconductor. Within the conductor the wave has, as might be expected, anintrinsic velocity of propagation just appropriate to the averagetransverse seesaw dielectric constant. Thus, if the regionwithinwhichthe electromagnetic wavepropagates is completely filled'wtih thecomposite conductor, the condition on the velocities.

principle. The entire region between the sheath 151 andthe core 152(which may be either of solid tubular metal, either magnetic ornon-magnetic, or of dielectric material), is filled with alternatelaminae of thin metal and dielectric cylinders 153 and 154,respectively. The metal laminae are, as in the embodiments describedabove ,using laminated structures, made as thin as possible comparedwith the skin depth 8. The dielectric laminations are also made verythin compared to '6 and, as pointed out above, in many'cases it ispreferable to make them smaller than the metal laminations. Themateriallof which the dielectric laminations are made is not criticalbut is bestv chosen to have high insulating power and low dielectricconstant.

In Fig. 15, an approximate curve of current density within thetransmission line 150 vs. radial distance is shown. It will be observedthat in the outer layers, current flows in one direction, and that inthe inner layers it flows in the opposite direction. The attenuation ofsuch a transmission line 150 is much less than the attenuation of aconventional line of equal outside dimensions.

Fig. 16 shows an antenna structure which is somewhat similar to that ofFig. except that it embodies, or is coupled to, a composite cable of thetype shown in Fig. 14. In the arrangement of Fig. 16, the inner half ofthe stack 150A comprising the metal laminations 153 and insulatinglayers 154, extends out, by substantially onequarter of a wavelength inthe dielectric of the frequency to be radiated past the point where theouter portion of the stack 150B is shaped to form a circular skirt 150Csurrounding the stack 150 and extending back, as shown in the drawing, adistance substantially one-quarter wavelength in the dielectric of thefrequency. Surrounding the members 150A, B, C and D is a mass 155, whichmay be rounded at the end, of dielectric material having a dielectricconstant which matches the average dielectric constant of the compositeconductor 150. The radiation pattern of the antenna of Fig. 16 is quitesimilar to that of the structure of Fig. 10. The advantages of low skineffect loss in the antenna structure and ready coupling to a compositeconductor of the laminated type are similar to those of Figs. 9 and 10.

The manner in which the various antenna structures described above canbe coupled to coaxial cables and other lead-in members is described inthe parent application in which is also described ways of makingcomposite conductors forming parts of the antenna structures disclosedherein. It is obvious that many changes can be made in the embodimentsdescribed above. The various embodiments and the modifications thereofdescribed herein are meant to be exemplary only and they do not by anymeans comprise a complete list of conductors to which the presentinvention is applicable and it is obvious that many more will occur tothose skilled in the art. It is intended to cover all such obviousmodifications as clearly fall within the scope of the invention.

What is claimed is:

1. An antenna comprising first and second conducting members, at leastone of said members being a composite conductor comprising a pluralityof elongated conducting portions spaced by means including insulatingmaterial, each of said conducting portions having at least one dimensionin a direction substantially transverse to the direction of wavepropagation along the length thereof which is small compared with itsappropriate skin depth at the frequency of electromagnetic wave to beradiated therefrom, said composite conductor extending in a directionaway from the antenna end of the other conductor and defining aradiation element of said antenna, said composite conductor beingembedded beyond the end of said other conductor in dielectric materialhaving a dielectric constant of a value to produce a velocity ofpropagationtherein which matches that of the wave in said compositeconductor.

2; The combination of elements as claimed in claim 1 wherein saidelongated conducting portions are laminations.

3. The combination of elements as in claim 1 in which said elongatedconducting portions are of filamentary material. V

p 4; The combination of elements as in claim 1 in which said elongatedconducting portions are in the form of thin cylinders positioned withinand coaxial with said other conducting member, said other conductingmember being a solid metal cylinder which terminates in a solid circularplate. I

'5. The combination of elements as .in claim 1 in which said elongatedconducting portions are in the form of thin cylinders positioned withinand coaxial with said other conducting member, said other conductingmember being a solid metal cylinder which terminates in a circularskirt.

6. The combination of elements as in claim 1 in which said elongatedconducting portions are in the form of thin cylinders positioned withinand coaxial with said other conducting member, said other conductingmember being a solid metal cylinder which terminates in a circular skirtof a length substantially one-quarter wavelength in the insulatingmaterial of the frequency to be radiated.

7. The combination of elements as in claim 1 in which said elongatedconducting portions are in the form of thin cylinders positioned withinand coaxial with said other conducting member, said other conductingmember being a solid metal cylinder which terminates in a circular skirtof a length substantially one-quarter wavelength in the insulatingmaterial of the frequency to be radiated, the thin cylinders extendingbeyond the beginning of the skirt for a distance substantiallyone-quarter of a wavelength in the insulating material of thisfrequency.

8. An antenna comprising as a radiation element thereof a multiplicityof elongated conducting portions spaced by means including insulatingmaterial, each of said conducting portions having at least one dimension.in a direction substantially transverse to the direction of wavepropagation down the length thereof which is small compared with itsappropriate skin depth at the frequency of electromagnetic wave to beradiated therefrom, said elongated conducting portions being in the formof thin cylinders positioned within and coaxial with an outer solidmetal cylinder which terminates .in a solid circular plate, the thincylinders extending beyond the surface of the plate for a distancesubstantially one-quarter of a wavelength in the insulating material ofthe frequency to be radiated.

9. An antenna comprising as a radiation element thereof a firstconductor, a second conductor, and a third conductor which is at leastas thin as the skin depth of penetration of waves at the frequency ofoperation of said antenna and which is spaced parallel from said firstand second conductors by first and second dielectric materialsrespectively said first and third conductors extending in a directionaway from the end of said second conductor, said first and thirdconductors being imbedded beyond the end of said second conductor in adielectric material having a dielectric constant of a value to produce avelocity of propagation therein which substantially matches that of thewave traveling in said first and third conductors.

10. The combination of elements as in claim 1 in which said elongatedconducting portions are in the form of thin cylinders positioned withinand coaxial with said other conducting member, said other conductingmemwhich said first and second conducting members each itqsllhstgnfialy- .Oge-quarte wavelength inthe .incomprise a plurality of elongatedconducting p0 s eueney to be radiated by the spaced by means includinginsulating mate a1 and sat 9 eylindei's terminating in conductingportions are arranged in two of par: 1 the cylinders, the skirt and theallel positioned portions in the shape of a dipole. .5 vs ll f flr ndedby dielectric mate- 12. The combination of elements as in claim 1 inwhich said first and second conducting member each comprise a pluralityof elongated conducting portions spaced means including insulatingmaterial and said conducting portions are arranged in two groups ofparallel positioned 10 portions in the shape of a dipole with endspointing in opposite directions. 1

' 13. The combination of elements as in claim 1 which said first andsecond conducting members each comprise a plurality of elongatedconducting portions 15 spaced by means including insulating material andsaid conducting portions are in the form of thin coaxially arrangedcylinders forming one of said conducting bers and, the inner half ofsaid cylinders extending beyond the outer half of said cylinders by adistance correspond- 2 0 thfi s of h patent Dec. 23, 19,47 Jan. 6, 1948June 13, 1950 Nov. 28 1950 Aug. 12, 1952

